CA2235669A1 - Method for source transfer in a wireless telecommunications system - Google Patents

Abstract

In a wireless telecommunications system comprising a mobile switching center and at least two base stations, control of a selection/distribution unit (SDU) is passed from a source base station to a target base station during source transfers. More particularly, the target base station establishes a packet-based connection with the SDU so that control information relating to an active mobile call may be transferred from the source base station to the target base station via the SDU with the target base station then taking the role of the source base station in the call. Upon completion of the source transfer, the source base station disconnects the link based on the second interconnection protocol from the SDU.

Description

CA 0223~669 1998-04-23 METHOD FOR SOURCE TRANSFER IN A
WIRELESS TELECOl\/IMUNICATIONS SYSTEM

Cross Reference to Related Application:
This application is related to the applications of:
Michael F. Dolan, Thomas L. McRoberts, Eshwar Pilk~npalli and Thomas T.
Towle entitled "Wireless Telecommunications System For Improving Performance And Compatibility";
Deborah L. Barclay, Michael F. Dolan, Thomas L. McRoberts and Thomas T.
10 Towle entitled "Method For Handoff Type Selection By A Target Base Station In A
Wireless Telecommunications System"; and Michael F. Dolan and Thomas T. Towle entitled "Method For Addressing Call Glare In Wireless Telecommunications Systems" which applications are assigned tothe assignee of the present application, and are being filed con~ lly herewith.
15 Technical Field:
This invention relates to wireless teleco~ ications networks, and more particularly, to source transfer among base stations in such wireless telecommunications networks.
Background of the Invention:
The world-wide proliferation of wireless telecommunications presents an opportLmity for service providers positioned to benefit from an ever-growing demand for convenient, reliable wireless service. As these service providers are well aware, controlling expenses while providing such service, via the procurement and mai~llenallce of state-of-the-art wireless telecomlnullications eq-lipm~nt poses a 25 significant challenge. Fxi.cting wireless service providers meet this challenge by implementing wireless telecommunications networks comprised of mobile switching centers (MSCs) interconnected to base stations. The MSC completes calls between mobile stations (that is, any mobile terminal using radio tr~n~mi~.sion) and other parties. These "other parties" may be mobile stations or parties served by the public-30 switched telephone network. Each base station is associated with a specific geographic region and is an interface between mobile stations within its region and the MSC.
A common occurrence in existing wireless telecollllllunications systems is the need to transfer call control (hereinafter, referred to as source transfer) from a first 35 base station to a second base station as a mobile user travels from one geographic region to another. Source transfer requires precise and rapid communication among the mobile switching center and the affected base stations. Fxi~tin~ wireless CA 0223~669 1998-04-23 telecommunications equipment places severe limitations on the ability of serviceproviders to devise various network configurations which might enhance the efficiency of source transfer. This is because telecommunications equipment vendors use rigid mobile switching center/base station interconnection protocols and routinely 5 dispose integral functions in a number of systems which inhibits the ability of networks to pass call control among base stations. As a result, it is impossible to choose and allocate, on a call-by-call basis, individual network components for supporting source transfers. Indeed, service providers cannot create, either call-by-call or network-wide, a customized wireless telecommunications configuration for 10 exploiting a synergy or minimi~inp problems associated with source transfer in a particular geographic region. Re~L,dilling the use of wireless telecommunications equipment for source transfer raises the cost of doing business for all wireless service providers. These costs and inconveniences associated therewith are ultimately borne by wireless service subscribers. Therefore, there is a need in the art for enhancing the 15 efficiency with which source transfers are accomplished in wireless telecommunications networks.
Summary of the Invention:
This need is addressed and a technological advance is achieved by interconnection protocols for supporting packet switched messages between the MSC
20 and base stations in wireless telecommunications systems. More particularly, a first packet interconnection protocol establishes an interface b~lw~ll a selection distribution unit (SDU) for performing frame selection and voice transcoding, and a base station interconnection processor for ll~lslllillhlg sign~ling and user data to mobile stations. A second packet interconnection protocol establishes an interface 25 between the SDU and a base station controller for transmitting control information.
In a prc;r~ d embodiment of the present invention, a wireless telecG ll~ications system includes a mobile switching center which serves at least two base stations. To transfer call control from a first (source) base station to a second (target) base station, the source base station extends a handoff request message to the 30 mobile ~wilching center for forwarding to the target base station. A packet-based connection is established between the selection/distribution unit (SDU) associated with the call and the target base station. Control information is then exchanged to accomplish source transfer from the source base station to the target base station.
Advantageously, a single, centrally accessible SDU accomplishes all processing 35 necessary for the source transfer. Multiple SDUs are not required. In other words, the functionality of the SDU need not be duplicated in each base station as is required in existing wireless telecommunications systems.

- CA 0223~669 1998-04-23 B~ef Description of the D~ a~
FIGs. 1-4 are illustrative embo-1iment.s of wireless telecommunications systems in which the present invention may be practiced;
FIG. 5 is a message flow diagram of mobile station call origination as 5 performed in the wireless telecommunications system of FIG. 1;
FIG. 6 is a message flow diagram of soft handoffsource transfer as p~lrolllled in the wireless telecolllmul~ications system of FIG. 3;
FIG. 7 is a message flow diagram of inter-base station communications for soft handoff support as p~ lrolllled in the wireless telecommunications system of FIG. 3;
FIG. 8 is a message flow diagram of handoff type selection by a target base station as p~,.rolllled in the wireless telecoll.~ ~ications system of FIG. 3;
FIG. 9 is a message flow diagram addressing call glare as performed in the wireless telecommunications system of FIG. 3;
FIG. 10 is a message flow diagram of ~ign~ling connection clearing by a target base station as ~t;lrolllled in the wireless telecon~llul~ications system of FIG. 3.
Detailed De~ ."tion:
FIGs. 1-4 are illustrative embo-liment~ of wireless telecommunications systems in which the present invention may be p ~cticed. Although four embo(liment~
are shown for clarity, those skilled in the art will recognize that the first and second packet inlel~;o~ ection protocols may enable numerous other arrangements of wireless telecon~ ications systems.
FIG. 1 is a simplified block diagram of wireless telecoll"nul~ications system 100 including mobile switching center (MSC) 102, first base station 110 and second base station 120. MSC 102 includes control processor 104 for executing tasks associated with call control and mobile station mobility management. Control processor 104 is interconnected to call control processors of the first and second base stations via ~ipn~lin~ links 131 and 133, respectively. In alternative embodiments, ~i~n~lin~ links 131 and 133 resources are conserved by multiplexing into a common channel for accessing control processor 104 of MSC 102. Switch fabric 106 is intercol"~e~;led to SDU 108 via user traffic (voice/data) link 135. In this embodiment, SDU 108 provides frame selection and voice coding for all base stations in wireless network 100 (in this example, base stations I l O and 120).
First base station l lO comprises call control processor 112 for ~mini~tering functions associated with call origination and termin~tion~ and controlling SDU 108 on a call-by-call basis; interconnection processor 114 for mapping proprietary connections 137 into the standard user traffic interface 139 to the SDU; and channel element 116 for establishing communications between the base station and subscriber CA 0223~669 1998-04-23 equipment, such as mobile station 160. Call control processor 112 and interconnection processor 114 communicate wvith channel element 116 over proprietary int~ ces 137, as known in the art. SDU 108 is interconnected to intelco~ e~;lion processor 114 via a first packet interconnection protocol over packet transport-based link 139. SDU 108 is also interconnected to call control processor 112 via a second packet interconnection protocol over packet transport-based link 143 for allowing first base station 110 to control SDU 108, as necessary.
Similarly, second base station 120 compri~es call control processor 122, interconnection processor 124 and channel element 126. Call control processor 122 10 and interconnection processor 124 conmlul~icate with channel element 126 overproprietary int~ ces 129. Interconnection processor 124 is interconnected to SDU108 via a first packet interconnection protocol over packet transport-based link 141 and call control processor 122 is interconnected to SDU 108 via a second packet interconnection protocol over packet ll~l~olL-based link 145. Call processor 112 and 15 call control processor 122 communicate directly via ~ign~ling link 105.
In this illu~l~d~ive embodiment, SDU 108 is positioned within MSC 102. The separation of the SDU function from a base station and its centralization enh~n~es the ability of service providers to enhance the efficiency of exi~ting call processin~
functions as described below.
FIG. 2 is a simplified block diagram of wireless teleco~ ications system 200 including mobile switching center 202, first base station 220 and second base station 240. Also shown is mobile station 260 served by the first base station. Mobile switching center 202 includes call control processor 204 and switch fabric 206. Call control processor 204 is interconnected to call control processors of the first and 25 second base stations via .~i n~ling links 201 and 203, respectively. Switch fabric 206 is interconnected to SDU 224 (positioned within the first base station) via user traffic (voice/data) link 209. In this embodiment, SDU 224 provides frame selection and voice coding for all calls initi~te~l or handed off by means of hard handoff to base station 220.
First base station 220 comprises call control processor 222, SDU 224 and channel element 226. Channel element 226 is interconnected to the rest of the components within the base station via proprietary intçrf~ es 227. Second base station 240 comprises call control processor 242 and hl~rcol~l ection processor 244 which are interconnected to channel element 246 via proprietary interfaces 247. In this 35 embodiment, SDU 224 not only serves the first base station but is shown interconnected to call control processor 242 and interconnection processor 244 of the second base station via packet transport -based ~i~n~ling and user traffic link 233, and CA 0223~669 1998-04-23 packet transport-based ~i~n~ling link 231, respectively. Sign~ling link 231 allows SDU 224 to be controlled by other base stations while ~ign~lin~ and user traffic link 233 enables co~ nullication of coded voice between a base station (in this case,second base station 240) and an SDU located in a dirrelclll base station (in this example, first base station 220) on a call by call basis. Although SDU 224 is shown positioned within first base station 220, second base station 240 may include the SDU
in alternative embol1imenti. Further, in alternative embo~1iment~, a common sign~ling channel is created by multiplexing multiple instances of ii~n~ling link 205 into a single int~rf~ce between base station 220 and call control processor 204 of MSC 202, lO or multiple in~t~n~es of ~iFn~ling link 207 into a single interface between base station 240 and call control processor 204.
FIG. 3 illustrates a network configuration embodiment in which the SDU
function is located independently of both the MSC and base stations. In this embodiment SDU 310 provides frame selection and voice coding for all base stations 15 in wireless network 300 and can be ~cces~ed by multiple base stations. More particularly, wireless telecommunications system 300 comprises mobile switching center 302, SDU 310, first base station 320, and second base station 340.
MSC 302 comprises control processor 304 and switch fabric 306. In this embodiment, control processor 304 is interconnPcted to first base station 320 and 20 second base station 340 via si~n~ling links 301 and 303, respectively. SDU 310 is interconnected to switch fabric 306 of MSC 302 via user traffic link 307. SDU 310 also ,,.~i"~ c packet transport-based user traffic and ~ign~ling links 313 and 315 to interconnection processors associated with first base station 320 and second base station, respectively. Packet transport-based ~ign~ling links 321 and 323 are subject to 25 the second interconnection protocol and allow first base station 320 and second base station 340, respectively, to control the SDU when necessary as described in detail below.
First base station 320 comprises call control processor 322, interconnection processor 324 and channel element 326. Channel element 326 collllllullicates with 30 other components within the base station over proprietary links 327. In this embodiment, first base station 320 serves mobile station 360. Similarly, second base station 340 comprises control processor 342 and interconnection processor 344 which are connected to channel element 346 via proprietary interfaces 347.
Packet transport-based user traffic and ci~n~ling links 313, 315 are subject to 35 the first interconnection protocol and enable the communication of coded voice and associated ~i~n~lin~ between the base stations and SDU 310 on a call by call basis. In alternative embodiments, multiple instances of si~n~ling links 301 and 303, CA 0223~669 1998-04-23 respectively, may be multiplexed into common ~ign~ling channels to reduce the overall number of .~i~n~lin~ links which may be transmitted by the system. Call control processor 322 and call control processor 342 can con~ icate directly viasign~lin~ link 305.
FIG. 4 is a simplified diagram illustrating yet another embodiment of the present invention including an "hltel~volking processor" for performing functions associated with transforming data from a format used within the public switched telephone network to one used across an air interface.
Wireless telecollJl,.u.lications system 400 comprises MSC 402, interworking 10 processor 410, SDU 420, first base station 430 and second base station 440. MSC 402 includes control processor 404 which co.."llu,licates with the call control processors 432 and 442 of first base station 430 and second base station 440, respectively, via ~ign~ling links 403 and 405, respectively. Also shown is switch fabric 406 which is interconn~cted to illlel~JlLng processor 410 via user data traffic link 407. In turn, interworking processor 410 is connected to SDU 420 via user data traffic link 411.
SDU 420 provides frame selection and tçrmin~tion of the radio link protocol used for data tr~n~mi~.~ion for all base stations in wireless network 400. SDU 420 m~int~in~
packet transport-based links to the first and second base stations, as described below.
First base station 430 comprises call control processor 432 and interconnection processor 434 which collllllullicate with channel element 436 over proprietary interfaces 437. Also shown is mobile station 460 served by the first base station 430.
In this embodiment, call control processor 432 is hll~lcol~llected to SDU 420 via packet transport-based l;nk 413 which is subject to the second interconnection protocol. Interconnection processor 434 is hll.,lcolmected to SDU 420 via packettransport-based link 415 subject to the first inlelcolmection protocol. Second base station 440 comprises call control processor 442 and interconnection processor 444 which are connçcted to channel element 446 via proprietary interface 447. Call control processor 442 is interconnected to SDU 420 via packet transport-based ~i~n~lin~ link 417 while ~ com1ection processor 444 is connected to the SDU via packet transport-based link 419. Signslling links 413 and 417 allow each base station to control SDU 420 as n~cess~. ~ for various processes including call handoff.
Sign~ling links 415 and 419 enable the co.lllllunication of coded data and associated ~ign~lin~ between each base station and the SDU on a call by call basis. Call control processor 432 and call control processor 442 can cO~ icate directly via ~ign~ling link 405.
The central, and independent location of interworking processor 410 and SDU
420 allows wireless service providers great flexibility in network configuration since CA 0223~669 1998-04-23 the functionality associated with these two processes can be accessed by a number of base stations. In other words, allocation of the interworking process and the SDU
function on a per base station basis is not required. Although interworking processor 410 is shown in a central location, alternative embodiments may deploy the interworking processor in many other locations, such as a base station, MSC or within the SDU.
The above-described illustrative embo-liment~ are presented to exemplify the network configuration flexibility enabled by the first and second packet interconnection protocols for communication between the MSC and base stations vi an 10 SDU. Although the most common implementations of the present invention have been shown, those skilled in the art may devise numerous other arrangements using these packet transport protocols.
Predictably, the first and second packet transport illhlcontlection protocols which enable the location flexibility also affect call proces~ing. To exemplify the 15 impact on existing call processes, a series of message flow diagrams is presented in FIGs. 5-10. For purposes of clarity, each message flow diagram is associated with a wireless telecollllllul~ications system depicted in FIGs. 1-4. Although the association with a wireless telecolll-llul,ications system is made for clarity, those skilled in the art will recognize that these messages may be deployed in any number of wireless 20 network configurations.
FIG. 5 is a message flow diagram depicting the exch~n~e of messages required for origination of a call from a mobile station to another party. For purposes of example, assume that the messages described below are exchanged within wireless telecommunications system 100 as shown in FIG. 1. In this example, a user 25 associated with mobile station 160 wishes to place a call to another party (not shown).
Accordingly, mobile station 160 transmits an origination message to its serving base station (t_at is, base station 110). Base station 110 receives the origination message and extends a service request message to MSC 102 over si~n~lin~ link 131. In response to this service request message, base station 110 receives a connection30 Co~ ion message from MSC 102 over si~n~ling link 131. Subsequently, MSC
102 sends an ~signment request message to base station 110 over ~ign~ling link 131.
After base station 110 receives the ~csignment request message from the mobile switching center over iign~ling link 131, base station 110 assigns radio resources to the call and initi~tes a packet transport based channel establi~hment procedure for 35 sign~ling between call control processor 112 and SDU 108 over ~ign~ling link 143 to allow base station 110 to control SDU 108. Base station 110 also establishes a packet transport based communication link 139 between interconnection processor 114 and CA 0223~669 1998-04-23 SDU 108. Subsequently, base station 110 establishes a traffic channel with mobile station 160 and a call connection is made. Base station 110 extends an ac.~ignment complete message to MSC 102 over ~i~n~ling link 131 to indicate that it considers the call to be in a "con~ alion state." In the prere.l~d embodiment, the ~signment S complete message includes a time parameter which indicates a more nearly exact time at which the mobile began to use the traffic channel. Advantageously, this time of origination allows the service provider to more accurately bill for the call.
FIG. 6 is a message flow diagram depicting messages exchanged during soft handoff source transfer occurring when a user of a mobile station travels outside of the 10 geographic area of a first base station. For purposes of this example, assume that the mobile station is mobile station 360 served by wireless telecollll,lullications system 300 shown in FIG. 3. Also assume that the mobile station is traveling out of thegeographic region served by the first base station 320 (also known as the "source"
base station) to the geographic area served by second base station 340 (also known as 15 the "target" base station). Initiation of call control Lld.~r~. from the source base station to the target base station is commenced when source base station 320 realizes that source transfer is necessary and extends a soft handoff source transfer message to MSC 302 over ~ign~ling link 301. MSC 302 rec~ves the soft handoffsource transfermessage and fo.~v~ds it to target base station 340 over sign~ling link 303. The soft 20 handoffsource transfer message includes information identifying the call cullellLly served by source base station 320. In this example, assume that target base station 340 determines that it will accept the source transfer (in alternative embo~liment.~, the target base station may decline to accept the source transfer call). Accordingly, target base station 340 extends a packet connection request message to SDU 310 to create 25 ~ign~ling link 323 in response to receiving the soft handoff source transfer message from MSC 302. The packet connection request message çxten-le~l to the SDU
includes infollllalion which uniquely identifies the call currently served by the source base station. SDU 310 then sends an acknowledgme~t message to target base station 340. Target base station extends a soft handoff source transfer acknowledgment 30 message to MSC 302 via ~i~n~lin~ link 303. Subsequently, MSC 302 forwards thesoft handoff source transfer acknowledgment message to source base station 320 over .sign~ling link 301. In alternative embo~liment~, the soft handoff source transfer message could have been sent directly from the source base station 320 to the target base station 340 across sign~ling link 305. The soft handoffsource transfer 35 acknowledgment message could also have been sent across .sign~ling link 305. Upon receipt of the soft handofftransfer acknowle.lgment message, source base station 320 extends a transfer prepare message to SDU 310 over link 313. SDU 310 responds CA 0223~669 1998-04-23 with a transfer prepare acknowledgment message to source base station 320 indicating its re~-liness for source transfer. Upon receipt of the transfer prepare acknowledgment message, base station 320 sends a source transfer commit message across signaling link 321 to SDU 310 to cause the ~ sr~ of call control. SDU 310 forwards the source ll~lsfel commit message to target base station 340 over sign~ling link 323.
Target base station 340 then responds to the SDU with a source transfer commit acknowle~lgmrnt message indicating that it now has control of SDU 310. SDU 310 forwards the source transfer commit acknowle~lgment message to base station 320 across si~n~lin~ link 321. Next, target base station 340 sends a soft handoffsource 10 transfer complete message to MSC 302 via ~i~n~lin~ link 303. This message notifies the MSC that base station 340 now has control of the call which was previously served by base station 320. Base station 320 then disconnects its connection 321 with SDU
310.
FIG. 7 is a message flow diagram outlining the messages exch~nged among 15 base stations during soft handoffadd target procedures. "Soft handoffadd target"
refers to the process in which additional base stations become involved in the connection to the mobile station without disruption to the voice link. A traditional soft handoff scenario requires base stations participating in the handoff to exchange required control data. These control messages are passed b~lw~en the base stations 20 via the MSC. The latency introduced due to this procedure often does not meet the stringent timing requirements for successful soft handoff in a wireless teleco~ nullications system. FIG. 7 illustrates direct base station to base station comnlul~ications designed to improve the timing for the exrl~nge of data and thus, allow for con~i~t~ntly s~cces~ful soft handoffs. For purposes of example, assume that 25 the messages described below are exchanged within wireless telecommunication system 300 as shown in FIG. 3. For clarity, first base station 320 will be referred to as the "source" base station indicating that it is the base station which ~ ly has control of a call to which second base station 340 (also referred to as the "target" base station) is to be added. In accordance with the plef~lled embodiment, source base 30 station 320 ~letermin~s that a handoff is required and issues a handoff request message to target base station 340 via sign~ling link 305. Target base station 340 determines that it will accept the handoff. Accordingly, interconnection processor 344 in the target base station extends a packet-based connection request to SDU 310 to create sign~ling and user traffic link 315. SDU 310 completes connection 315 and returns a 35 connection acknowledgment message to target base station 340 indicating that the connection has been established.

CA 0223~669 1998-04-23 Target base station 340 then extends a handoffrequest acknowledgment message to source base station 320 over si~n~ling link 305. SDU 310 begins to send packetized user traffic messages to target base station 340 across link 315 immediately after the connection acknowle~lgment message is sent. In turn, the target base station 5 channel element 346 extends forward traffic channel data frames to the mobile station participating in the call which is being handed off. Upon receiving the first forward traffic channel data frame, target base station channel element 346 begins to send reverse idle frames to SDU 310 via interconnection processor 344 over link 315.
Upon determin~tion by SDU 310 that link 315 to base station 340 is al)pl.p,iately 10 established, the SDU extends a packet-based connected message to source base station 320 via sign~ling link 321. Subsequently, source base station 320 extends a handoff direction message to the mobile station participating in the call. More particularly, source base station 320 sends a sign~ling message to SDU 310 co~ llg a handoff direction message. SDU 310 sends the handoff direction message to the mobile station via link 313 which is internally connected to base station channel element 326.
The mobile station extends a mobile station acknowle-lgm~nt order to acknowledgethe handoff direction message received. The mobile station acknowledgment order is delivered to SDU 310 via si n~ling link 313. SDU 310 then informs source base station 320 of successful delivery of the handoff direction message via a data forward .sign~ling delivered message which is sent on sign~ling link 321.
The mobile station extends a handoff completion message to SDU 310 via links 327/313 and 347 /315 after completion of the soft handoffto the target base station. Subsequently, the SDU fol~v~ds the handoffcompletion message to source base station 320 via si~n~lin~ link 321 and source base station 320 extends a handoff performed message to MSC 302 via sign~ling link 301 to inform it that the mobilestation's active location has been changed.
The introduction of the first and second hll~rconnection protocols enables several types of call handoffs in a wireless teleconllllullications system as the mobile station moves from one base station to another. More particularly, the various types of handoff which occur include hard handoff, semi-soft handoff, soft handoff and soft handoffwith consolidation. In the plef~lled embodiment, when a target base station receives a request from a source base station indicating that a handoff of a call is requested, the target base station d~t~ . ."il~es which resources are available for the call.
For example, the source base station may request a soft handoffbut the target base station may only have resources for a hard handoff. This resource data is conveyed to the source base station so that agreement of the handoff type is reached before the handoffprocedure is commenced.

CA 0223~669 1998-04-23 FIG. 8 is a message flow diagram depicting the messages exchanged in wireless telecommunications system 300 for detçrmining handofftype selection by a target base station. In the plere.led embodiment, the source base station may allow one or more handofftype options which are conveyed to the target base station. This S particular embodiment supports both a m~n-l~te-l handofftype (i.e., the source base station allows only one handoff) or multiple handofftypes. Advantageously, there is a reduction in the number of messages exchanged during a handoff scenario due to an increased efficiency in the handoffexecution as a result of the handofftype selection process. Further, all the handoffmessages including the list of allowed handofftypes 10 can be circulated through the MSC across ii~n~ling links 301 and 303, thereby also allowing the MSC to exercise control ofthe handofftypes allowed.
For purposes of example, assume that control of mobile station 360, ~;u~ lly served by source base station 320, requires a handoff. The handofftype selectionprocess begins when call controller 322 of source base station 320 extends a handoff 15 required message to MSC 302 via ~i~n~ling link 301. MSC 302 receives the handoff required message and extends a handoffrequest message to call controller 342 of target base station 340 over ~i~n~ling link 303. The handoffrequest message includes a list of allowed handofftypes as formulated by call controller 322 of the source base station.
Target base station 340 determines which, if any, of the handofftype options it will select to process this call. If the target base station det~nnines that it may accommodate the requested handoff, interconnection processor 344 extends a connect message to the SDU to establish user traffic and sign~lin~ link 315. SDU 310 responds to the col~le-;l message by establishing ~ign~ling link 315 to interconnection 25 processor 344 of the target base station. Next, the target base station remains idle while waiting to receive forward traffic channel frames from the source base station.
As soon as the first forward traffic channel data frame is received in target base station channel element 346, channel element 346 begins to send reverse idle frarnes to SDU
310 via links 315 and 347. Upon receipt of the idle frames, SDU 310 detçnnines if 30 the connection bclw~ell the mobile station and channel element 346 of the target base station has been applopliately established and SDU 310 extends a packet connection established message to source base station 320 via ~i~n~ling link 313. In addition, target base station call controller 342 extends a handoffrequest acknowledgment message to MSC 302 via si~n~ling link 303. MSC 302 then extends a handoff 35 comm~ncl message to source base station call controller 322 so that the handoffcan be completed.

CA 0223~669 1998-04-23 Another common occurrence in wireless telecommunications systems is referred to as "glare". A glare situation occurs when a user ~lle~ to make a call at the same time that another party is ~lle.l,l,ling to call the same user. Traditionally, wireless telecon~ ications systems have been unable to accommodate call glare. In other words, the mobile origin~te~l call is serviced by default. With the establishment of the first and second interconnection protocols, a call glare situation is detectable by both the MSC and the mobile station. However, it is the responsibility of the MSC to resolve the situation by allowing only one call to be connected. More particularly, when the mobile station has initiated a call and the MSC has elected to reject the 10 initiated call and instead deliver the incoming call to the mobile station, the MSC must transmit this inforrnation to the serving base station so that activities in the network may be synchronized. The base station must signal its acceptance of the delivery of the incoming call. In some embo-liment.~, the base station may reject delivery of the incoming call in which case the MSC must proceed to service the call ori~:in~ted by 15 the mobile user.
FIG. 9 describes how sign~ling between the MSC and a base station can be used to synchronize the network to a new call direction in glare situations (that is, how to allow a mobile initiated call to be interrupted for delivery of a call to the mobile).
For purposes of example, assume that the messages described in message flow 20 diagram FIG. 9 are exchanged within wireless telecoll,l"ul,ications system 300 as shown in FIG. 3. The process begins when mobile station 360 transmits an origination message over an air interface to its serving base station (in this example, first base station 320). Base station 320 acknowledges receipt of the origination message with a base station acknowle~lgment order which is delivered to the mobile 25 station. Subsequently, base station 320 extends a service request message to MSC 302 to create si~n~ling link 301 and to folv~d the origination request. MSC 302 responds to base station 320 with a connection confirm~tion message indicating establi~hment of link 301. In this embodiment, the service request message includes mobile identity information such as its electronic serial number. MSC 302 then extends an 30 ~si nm.ont request message to base station 320 requesting that the base station allocate radio resources for the call. The ~signment request message includes a call direction element indicating the MSC's desire to change the direction of the call from mobile origin~te~l to mobile t.?rmin~te-l In this embodiment, functions performed by SDU 310 are separated from the base station so MSC 302 identifies SDU 310 in its35 ~c~ignment request message. Upon receipt of the ~signment request message, base station 320 initiates the packet-based channel establishment procedure as described in FIG. 5. Next, base station 320 sends a channel ~.cignment message over the control CA 0223~669 1998-04-23 channel of the radio interface to initiate an establi~hment of a radio traffic channel to the mobile station. The mobile station and network then exchange necessary messages to acquire the mobile station and properly connect it.
After the radio traffic channel and packet mode channel have been established, base station 320 extends an ~c~ignment complete message to MSC 302 and indicatesits acceptance of the call direction change by including a call direction acknowledgment element. Base station 320 then extends an alerting message to themobile station to cause ringing at the station via established links. When the call is answered, a connect order is transmitted to base station 320. Base station 320 then 10 extends a connect message to MSC 302 indicating that the call has been answered at the mobile station and is in a convels~ion state.
FIG. 10 is a message flow diagram depicting messages exch~nged within wireless telecollll.lul~ications system 300 to remove unnece~s~ connections. More particularly, during operation of a call that makes use of a soft handoff, a target base 15 station may be supplying a set of resources to support the call. A ~ign~ling connection specific to the call is also created between the MSC and the target base station.
Traditionally, when resources at the target base station are no longer required, they must be removed from the call under direction of the MSC. In the pre~ d embodiment of the present invention, the target base station directly interacts with the 20 MSC to remove such a ~i~n~ling connection.
For purposes of example, assume that soft handoffhas occurred and resources at the target base station are no longer required. Accordingly, source base station 320 extends a soft handoffdrop target message to MSC 302 to be forwarded to target base station 340. Target base station 340 removes its packet connection 315 to SDU 310 25 and sends a soft handoffdrop target acknowle~lgment message to MSC 302 via link 303 to be rOl ~ded to source base station 320. Target base station 340, re~ ing that it has no more radio resources allocated to the call, sends a clear request message to MSC 302 to request clearing of ~ign~ling link 303.
MSC 302 extends a clear command message to the target base station to 30 instruct it to release the associated dedicated resource (that is, ~ign~ling link 303). In response to the clear command message, the target base station sends a clear complete message and releases ~ign~ling link 303. Note that in alternative embodiments, the soft handoff drop target and soft handoff drop target acknowle~lgment messages is exchanged via ~ign~ling link 305.
Advantageously, the first and second interconnection protocols allow flexibility in MSC/base station communications which enables the above-describednetwork configuration and call processing and control. Although the present invention has been illustrated using plcrc~l~d embodiments, those skilled in the art may devise other arrangements without departing from the scope of the invention.

Claims (5)

Claims:

1. A method for accomplishing source transfer in a wireless telecommunications system comprises:
a source base station determining that a transfer is required;
a target base station accepting a transfer request from the source base station;and exchanging control information among the source base station, the target base station and a system for frame selection and voice coding to coordinate the source transfer.

2. The method of claim 1 further comprising the source base station disconnecting from the frame selection and voice coding system a control connection from the system upon completion of the source transfer.

3. The method of claim 1 further comprising the target base station assuming control of a call.

4. A method for accomplishing source transfer in a wireless telecommunications system comprises:
a source base station determining that a source transfer is required;
a target base station accepting the source transfer from the source base station;
and exchanging control information among the source base station, the target base station and a system for frame selection and radio link protocol termination to coordinate the source transfer.

5. A method for accomplishing source transfer in a wireless telecommunications system comprises:
a source base station determining that a transfer is required;
a target base station accepting a transfer request from the source base station;and exchanging control information among the source base station, the target base station and a system for voice coding.